*{
	margin: 0;
	padding: 0;
}
.img1,.img2,.img3,.img4{
	margin-top: 60px;
	width: 100%;
	height: 70vh;	
	background-size:100% 100%;
	
		/* 图片内渐变，多个transparent利用了渐变叠加 */
	/* background-repeat: space; */
	background-size: cover;
}
/* linear-gradient透明度,to bottom 自底部,transparent渐变 */
.img1{ background: linear-gradient(to bottom, transparent, transparent, transparent, transparent, black),
	    url(../imgs/1.jpg) no-repeat center;}
.img2{ background: linear-gradient(to bottom, transparent, transparent, transparent, transparent, black),
	    url(../imgs/2.jpg)no-repeat center;}
.img3{ background: linear-gradient(to bottom, transparent, transparent, transparent, transparent, black),
	    url(../imgs/3.jpg)no-repeat center;}
.img4{ background: linear-gradient(to bottom, transparent, transparent, transparent, transparent, black),
	    url(../imgs/4.jpg)no-repeat center;}
#imgstime{
	left: 0;
	right: 0;
	z-index: 0;
	
}